Filament joint for electric lamps



C. SEVERIN Dec. 31, 1940.

I FILAMENT JO INT FOR ELECTRIC LAMPS Filed May 24, 1940 Fig.1.

Patented Dec. 31, 1940 FILAMENT JOINT FOR ELECTRIC LAMPS Carl Severin, Cleveland Heights, Ohio, assignor to General Electric Company,a corporation'of New York . Application may 24, 1940, Serial "No. 336,977

4 Claims.

My invention relates in general to electric in- "candescent lamps and similar devices comprising an electric energy translation element or filament sealed within an envelope. More particularlyany invention relates to an improved joint or connection between the filament and leading-in wires of such devices.

In making the joint or connection between the filament and leading-in wires of electric incandescent lamps particularly of the type used for automobile headlighting service, the common practice atpresent is to bend the inner end portions of the parallel leading-in wires at right angles so as to extend towards or away from each 10 other, and to weld the filament legs to the rounded surfaceof such bent portions with the filament legs extending substantially at right angles to such bent portions. Such a procedure is entirely feasible where the current rating of 20 the lamp is relatively low, for in such case it is permissible-'toemploy leading-in wires of relatively small size which can therefore be bent into the desired shape with more or less ease .and P without danger of cracking the glass stem into which the wires are sealed. However, in the case of lamps having a relatively high current rating, such as 7 or 8 amperes, it is necessary to employ relatively heavy leading-in wires of adequate cross-section to convey the required current to the lamp filament. Such heavy leads are difilcult to bend, and particularly so without cracking the glass stem into which they are sealed. For this reason it has been found impractical to follow the above mentioned procedure in forming the joints 35 between the filament legs and the leading-in wires of lamps of relatively high current rating; but even if such procedure were practical, the resulting joint would not possess sufiicient mechanical strength to withstand, for any great length of time, the stresses to which it would be subjected by the repeated expansion and contraction of the lamp filament during the heating and cooling of the same. Due to the insufiicient bearing between the filament and leading-in wire. the joint would prematurely loosen and thus gradually permit adjacent turns of the filament coil to become short-circuited, eventually resulting in the early burn-out of the filament. Furthermore, the contact area between the filament and leading-in wire of such a joint is relatively small so that the temperature of the metal at the joint, during lamp operation, would be relatively high. Such a high temperature also tends to loosen the Joint. .In addition, it is very apt to 55 cause an early burn-out of the filament at a point just above the joint, where a eutectic alloy of tungsten and nickel (the tungsten of the filament. and the nickel of the inner lead portions of the leading-in wires) is formed after a short period of lamp operation.

One object of my invention is to provide an improved joint or connection between the filament and leading-in wires of electric incandescent lamps and similar devices.

Another object of my invention is to provide 10 an electric incandescent lamp or similar device with a joint between the filament and leading-in wires of sufiicient mechanical strength to withstand the stresses to which it is subjected during operation of the device and which will not loosen during such operation.

A feature of the invention is the use of leadingin wires each having a flattened inner end provided at a predetermined point with a transverse ridge or raised portion, of appreciable extent lengthwise of the wire, across which ridge the filament leg is welded to thereby provide an extended bearing for the filament leg and to fix the contact point between such leg and the leading-in wire at a predetermined point along the length of such filament leg.

Further objects and advantages of my invention will appear from the following description of species thereof and from the accompanying drawing in which: i

Fig. 1 is a front elevation of an electric incandescent lamp having a filament joint construction comprising my invention; Fig. 2 is a fragmentary perspective view, on an enlarged scale, of the mountof the lamp shown in Fig. v1; Fig. 3 is a fragmentary side elevation, partly in section, of a filament joint construction comprising my invention shown on a greatly enlarged scale; and Fig. 4 is a fragmentary perspective view,

likewise on a greatly enlarged scale, of a filament joint construction comprising my invention.

Referring to Fig. 1, the lamp there shown is of the miniature type employed for automobile headlights and comprises a sealed bulb l0 containing a pair of coiled linear filaments H, H

of a suitable refractory metal, preferably tungsten. The said filaments are electrically connected at their ends to relatively heavy leadingin wires l3, l4, l5 having nickel inner lead portions which extend parallel to each other through a stem or insulating support It to the terminals l1, l8, IQ of a base 20. The filaments H, l2 are arranged parallel to each other in a plane at right angles to the. longitudinal axis of the envelope and are laterally offset with respect to 56 joint.

each other. Filament H has a rating of approximately 45 watts, and is disposed symmetrically about the lamp axis so that when the lamp is mounted within a conventional parabolic headlight reflector with the lamp axis coinciding with the axis of the reflector, the filament Ii will be disposed symmetrically about the reflector focal point and in the focal plane of such reflector. Filament lllserves as the main filament for the production of a driving beam. The auxiliary filament I2 is so arranged within the lamp as to be positioned above and laterally offset to one side or the otherof the main filament Ill when the lamp is mounted in the reflector. The filament l2 has a rating of and serves to produce a passing beam. The two filaments II and 12 are adapted to be separately energized, thus necessitating the three leadingin wires l3, l4 and I5. Leading-in wire I! serves as a common lead, and in order to provide separate connections for the two filaments II and I2, the said wire I! is provided with an L-shaped arm 2! welded or otherwise secured to the inner end portion thereof and having an upstanding leg 22 extending parallel to the three leading-in wires l3, and i5. -Filament H is connected at its ends to leading-in wires l3 and I5, while filament i2 is connected at its ends to leadingin wires l4 and to the arm 2| of leading-inwire [5. To carry the required current of "l to 8 amperes or thereabouts to the filaments II and i2, the leading-in wires l3, l4 and I5 and the arm 2! are made of relatively heavy wire of the order of 40 mils in diameter. The filaments H and I2 are preferably made of tungsten wire having a diameter of approximately 10 mils, and together with the leading-in wires l3, l4 and I5 and the stem l6, forms the mount structure for the lamp.

The ends of each filament ll, 12 are provided with straight and substantially parallel leg portions 23 which extend substantially parallel to the leading-in wires l3, I4 and I5 and are secured to their corresponding leading-in wires by a joint or connection according to the invention. As shown particularly in Figs. 2-4, the innermost end portions of each pair of leading-in or support wires are flattened in parallel planes for a distance of about 2 or 3 mm. back from the tip thereof, as indicated at 24. One of theflat sides 25 of each wire is provided with a transversely extending ridge or raised portion 20 adjacent the tip of such wire, the top surface 2! of which has an appreciable width, 1. e. a dimension lengthwise of the wire, at least equal to approximately the diameter of the leading-in wires, for instance, approximately 0.035 inch or thereabouts. As shown in Fig. 2, the ridges 26 on each pair of leading-in wires are preferably located on opposite sides of the flattened ends of such wires. The side walls 28 of the ridge are preferably tapered or flared outwardly so that the base of the ridge is broader than the top'suiface 21 thereof.

Each filament leg 23 is laid across the top surface 21 of the ridge on its corresponding leading-in wire at approximately right angles to such ridge, and then welded to the ridge by the passage of an electric current through the The current .fiow is continued until the nickel of theleading-in wire melts, whereupon the filament leg 23 sinks into the ridge 20 and the melted nickel flows up on each side of the filament leg, as indicated at 29 in Fig. 4. The result is a strong and secure joint between the approximately 30 watts filament leg and the leading-in wire. Due to the extended bearing between the filament leg 23 and the ridge 28, the joint the necessary mechanical strength to withstand the stresses to which it is subjected by the expansion and contraction of the filament coil during the heating and cooling of the same. Premature loosening of the joint, with resultant short circuiting of adjacent filament coils and early burn-out of the filament, is thereby practically eliminated. Furthermore, the flattening of the inner end portions of the leading-in wires increases the surface area of such portions and accordingly increasesthe heat dissipation therefrom so that the temperature of the metal parts at the joint, during lamp operation, is reduced. Such a reduction in the temperature at the joint therefore reduces the possibility of a premature bum-out of the filament at a point immediately adjacent the joint, where a eutectic alloy of tungsten and nickel is formed after a certain period of lamp operation.

- During the manufacture of the lamp mount, it is customary to trim or cut oil the inner lead portions of the leading-in wires to a definite length. Such a trimming operation isperformed after the ridges 20 have been formed on the leading-in wires. Inasmuch as the 'point at which the wires are trimmed is apt to vary for different wires or for different mounts, I have found it preferable to locate the ridges II at such a point on the leading-in wires as to be positioned a slight distance back from the tip of the wires after the latter are trimmed, for instance, a distance of 0.010 inch or thereabouts. In this manner, the trimming or cutting on of a part of the ridge 20, and a consequent decrease in the extent of the bearing between the filament leg 22 and the ridge 20 is entirely prevented. In addition, such a construction insures that the points of contact 30 (Fig. 4) between the filament legs and the leading-in wires are uniformly fixed for individual mounts. As a result, the corresponding filaments of individual mounts each have the same length of tungsten wire between their points of contact with the leading-in wires.

While I have shown and described the preferred form of the invention, it is obvious that various modifications are possible. Thus, instead of only one transverse ridge 20 across the flattened end of each leading-in wire, two or more such ridges may be provided at spaced points along the length of the wire. Likewise, the upper surface 21 of the ridge, instead of being smooth or fiat, may be provided with vshaped grooves extending transversely of the wire so as to present a saw-tooth appearance, or it may be roughened in any other desired manner.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A joint for the filament and leading-in wire of an electric lamp comprising a leading-in wire provided with a flattened end having a ridge' of appreciable width on one of the flattened sur-- faces thereof, and a filament having a leg portion disposed across said ridge and sunk into the top surface thereof and welded thereto.

2. A joint for the filament and leading-in wire of an electric lamp comprising a leading-in wire provided with a flattened end having a ridge of appreciable width on one of the flattened surfaces thereof, said ridge extending substantially transversely of said wire, and a filament having a leg portion extending substantially parallel to said leading-in wire and secured to the flattened end thereof, said leg portion being disposed across said ridge and sunk into the top surface thereof and welded thereto.

3. A mount structure for an electric lamp comprising an insulating support having a pair of substantially parallel leading-in wires extending therefrom, said leading-in wires being provided with flattened ends each having a ridge of appreciable width on one of the flattened surfaces thereof, said ridges extending substantially transversely of said wires, and a coiled filament located substantially in the plane of said leadingin wires and having leg portions extending substantially parallel to said leading-in wires and secured to the said flattened ends thereof, said leg portions being disposed across the said ridges and sunk into the top surface thereof and welded thereto.

4. A mount structure for an electric lamp comprising an insulating support having a pair 01' substantially parallel leading-in wires extending therefrom, the inner ends of said leading-in wires being flattened in substantially parallel planes and each having a ridge of appreciable width on one of the flattened surfaces thereof, the said ridges being arranged on opposite sides of said flattened ends and extending substantially transversely of said wires, and a coiled filament extending substantially transversely of .said leading-in wires and having leg portions extending substantially parallel to said leading-in wires and secured to the said flattened ends thereof, said leg portions being disposed across the said ridges and sunk into the top surface thereof and welded thereto.

CARL SEVERIN. 

